In our copending New Zealand applications: 236660, 244007, 247509, 264225, 270344 we have described this kind of battery and switches which control the charging and discharging of such batteries as the vehicle operates. The contents of these specifications are hereby incorporated by way of reference.
The conventional automotive SLI battery consists of six 2.1 volt Lead acid cells connected in series. The SLI battery has a number of functions that it must perform. Firstly it must be able to provide high amounts of current to the starter motor to start the vehicle. secondly, it must be able to supply a stable voltage to the ignition and fuel systems of the vehicle during starting. Thirdly it must be able to supply reserve current to the ignition and lights of the vehicle when the alternator is not providing current. Fourthly it must be able to supply current to power electrical accessories which draw current over long periods of time when the vehicle is not running.
Ideally the battery should have a life in excess of two years, and it must be able to provide enough energy to start the vehicle even in all weather extremes. Also the battery must be able to withstand being partially discharged without suffering significant capacity loss. Low in terminal resistance is a requirement for high energy output in a battery. Batteries with a very low internal resistance, due to the construction required to achieve this low internal resistance do not have particularly good deep cycle performance. Batteries with good deep cycling characteristics, usually do not have the high current capability required for starting vehicles at low temperatures. The battery must also be low in weight, small in size, and of as low a cost as possible to meet motor vehicle manufactures requirements. By incorporating two separate batteries, a deep cycle battery and a starter battery in a single case it may be possible to meet these requirements. We refer to the starter battery as the cranking battery (CRA) and to the deep cycle battery as the auxiliary (AUX) battery.
Normally when starting the engine of a vehicle at low temperatures the starter draws large amounts of current and the voltage at the battery terminal falls considerably. There may be sufficient energy to turn the starter motor however there may be insufficient voltage to properly power the ignition and fuel systems. A dual battery has two separate and independent voltage outputs, thus the starter motor can be supplied from the starter terminal of the battery and the ignition system can be powered from the other positive terminal of the battery. Thus the ignition system will receive a smooth voltage of approximately 12 volts even though the terminal voltage of the starter battery may fall below 5 volts during starting. This means that the starting performance using a dual battery can be superior to that of a single SLI battery.
Using a dual battery, it may be possible to allow one battery to be discharged while conserving energy in the other battery to start the vehicle.
There have been many attempts at putting two 12 volt series of cells into a single container, however none so far have been particularly successful, as the method for constructing the battery has been incompatible with standard battery manufacturing equipment or final manufactured form of the battery has been significantly different from that of a conventional SLI battery in terms of sizing or terminal layout and thus has had difficulty in fitting into an automobile.
In U.S. Pat. No. 3,475,221, Jordan describes a four terminal automotive battery with two parallel stacks of plates in each of the six cells in the battery. The disadvantage with such a simplistic arrangement is that should one stack of plates become discharged or fail then the other stack of plates which shares common electrolyte will also become discharged. As terms of art an element comprises positive and negative groups nested together with separators in place. A group is an assembly of plates of like polarity burned to a common strap.
In U.S. Pat. No. 3,758,345, Toth describes an automotive battery with a set of U-Shaped plates which constitute the main series of cells and a set of small rectangular plates which are accommodated in the space defined by the U in the large plate, which constitute the auxiliary series of cells. Because the cells share a common watering device, the electrolyte in the auxiliary cells is not separated from the electrolyte in the main cells.
U.S. Pat. No. 4,883,728 (Witehira) describes a 3-terminal automotive battery containing two 12 volt series of cells, with a common negative terminal in a single container. The design of battery that Witehira proposes has many inherent disadvantages. The provision of a common negative terminal makes it impossible to connect the batteries in series. Thus two 12 v batteries cannot be joined to make a 24 v source for trucks and special purpose vehicles. The design and layout of the proposed battery means that the positioning of the terminals is restricted. The construction of the proposed battery requires a total of 11 inter-cell welds as opposed to the 5 in a conventional 12 volt battery. The inter-cell welds are not all on the same axis so a single axis inter cell welder would not be suitable for manufacturing the battery. The plates and cell elements are placed in the battery in a North-South arrangement as opposed to the standard arrangement of laying the plates in an East-West fashion. Not only does this mean that most of the inter-cell welds are at right angles to those in a conventional battery but the plates are also laid in the battery at right angles to those in a conventional battery. The two positive terminals due to the close positioning of the two terminal cells, must be placed extremely close to each other. This has a number of disadvantages, notably that the terminal clamp on one terminal may short circuit the other terminal. Also if one terminal is at a higher potential to the other terminal and a thin film of liquid exists on the lid of the battery, electrochemical reactions may easily occur. Also due to the positioning of the terminal cells, the terminals are located in the middle of the battery, not the side as is usual. Thus it may be difficult for cable clamps to reach the battery terminal.
Examined Japanese Patent application 1-29022 in the name of Nippon Denso K.K. describes a 3-terminal automotive battery containing two 12 volt series of cells, with a common negative terminal in a single container. In this design they propose one series of cells with a larger capacity for starting the vehicle and another series of cells with a smaller capacity for providing a stable voltage to electrical equipment. The negative terminals of the two series of cells are internally connected to so that only one communal negative terminal extends from the case. Because the two series of cells are arranged side by side, conventional width plates cannot be used in the construction of this battery. Also because the plate widths are narrower than in conventional batteries, there are restrictions for casting the strap using a conventional group burning or cast on strap machine. The Battery contains 11 inter-cell wields, 10 of them are on the North-South axis and one of the on the East-West. Thus a multi access inter cell welding machines would be required on a production line. The battery has a common negative terminal so two of these batteries cannot be connected in series for 24 volt operation. The proposed battery does not provide for different construction methods in the two series of cells. Thus the cells are not optimized to provide deep cycling and starting functions and only a single plate type is used.
U.S. Pat No. 5,162,164 (Dougherty etal) and U.S. Pat. No. 5,002,840 (Klebenow etal) describe a 12 volt automotive battery with an external positive and negative terminal. The battery contains two series of six cells connected in parallel via a switch. The first series of cells is transposed along a first axis and the second series of cells is placed along a second axis transverse to the first axis. Bus bars are described for connecting the like terminals of the two series of cells. The bus bars are suspended between the battery lid and the battery case. The bus bars are covered by a chlorinated polyolefin plastic sleeve, which protects the bus bar from corrosion from the electrolyte, and allows them freedom of movement. The battery has only a single pair of terminals, thus it cannot provide two independent current sources simultaneously.
McDowall in U.S. Pat. No. 4,239, 839 describes a modular multicell battery wherein a barrier is inserted into mutually parallel array of identical plates (frames or separators). The barrier divides the cuboid container into two separate batteries each of which with its own volume of electrolyte. The position of the barrier partitions the plates into 33 the desired ratio in order to secure the selected outputs. the capacity is increased by adding more frames and separators.
EP 92106302 (Robert Bosch GmbH) uses two separate batteries mounted one on top of the other. One battery is a high current type for starting and the other is a deep cycle type for powering electrical accessories. Because the batteries are mounted one on top of the other, the access to the lower battery is hindered and this introduces servicing and testing difficulties.